Ultrasonic cleaning: Fundamental theory and application

Paresh Shah in the first part of the article describes the theory of ultrasonic technology and how its technology is applied to precision cleaning

Cleaning technology is in a state of change. Vapour degresing using chlorinated and fluorinated solvents along the standard for most of industry, is being faced out in the interest of the ecology of our planet. At the same time, cleaning requirements are continuously increasing.

Cleanliness has become an important issue in many industries where it never was in the past industry such as electronics where cleanliness was always important, it has become critical in support of growing technology. As a result, the cleaning industry has been challenged to deliver the much needed cleanliness and has done so through rapid innovation over the past several years.

Many of these advances have involved the used of ultrasonic technology. The cleaning industry is currently in a struggle to replace solvent degreasing with alternative ‘environmentally friendly’ means of cleaning. Although substitute water-based, semi-aqueous and petroleum-based chemistries are available, they are often less effective as cleaning than the solvents and may not perform adequately in some applications. Unless a mechanical energy boost is added to assure the required levels of cleanliness.

Ultrasonic energy is now based extensively in critical cleaning applications to both speed and enhance the cleaning effect of the alternative chemistnes. This paper is intended to familiarise the reader with the basic theory of ultrasonic energy can be most effectively applied to enhance a variety of cleaning process.

What is ultrasonic?

Ultrasonic is a science of sound waves above the list of human audibility. The frequency of the sound waves determines its tone or pitch. Low frequencies produce low or bass one and high frequencies produce treble ones. Ultra sound is a sound with a pitch so high that it cannot be heard by human ear. Frequencies above 18 kHz are usually considered to be ultrasonic. The frequencies used for ultrasonic cleaning range from 20,000 cycles per seconds or kHz or over 1,00,000. Most commonly used frequencies for industrial cleaning are between 20 kHz and 50 kHz. Frequencies above 50 kHz are more commonly used in table-top ultrasonic cleaners such as those found in jewellry shops and dental offices.

Enertech Electronics is supplier of ultrasonic cleaning equipment used for industrial and precision cleaning in a wide range of applications. With a 8-10 years of experience in the research and development of ultrasonic cleaning technology, the equipment the company designs and builds reflects its pioneering spirits and its commitment to design and manufacture more reliable ultrasonic parts cleaning systems.

Benefits in cleaning and rinsing process

Cleaning in most instance requires that a contaminant be dissolved (as in the case of soluble soil) or displaced (as in the care of a non-soluble soil) or both dissolved and displaced (as in the case of insoluble particulars being held by a soluble binder such as oil or grease). The mechanical effect of ultrasonic energy can be helpful in both speeding dissolution and displacing particles.

The medicinal effect of ultrasonic energy can be helpful in both speeding dissolution and displacing particles. Just as it is beneficial in cleaning, ultrasonic is also beneficial in the rinsing process. Residual cleaning chemicals are removed quickly and completed by ultrasonic rinsing.

As the cleaning chemistry dissolves the contaminant, as saturated layer develops at the interface between the fresh cleaning chemistry and the contamination. Once this has happened, cleaning action stops as the saturated chemistry can no longer attack the contaminant. Fresh chemistry cannot reach the contaminant.

In removing a contamination by dissolution, it is necessary for the solvent to come into contact with and dissolve the contaminant. The cleaning activity takes places only at the interface between the cleaning chemistry and the contaminant.

Ultrasonic caviation and implosion effectively displace the saturated layer to allow fresh chemistry to come into contact with contaminant remaining to be removed. This is especially beneficial wherein regular surfaces or internal passageways are to be cleaned.

Ultrasonic equipment

To introduce ultrasonic energy into a cleaning system requires an ultrasonic transducer and an ultrasonic power supply or ‘generator.’ The generator supplies electrical energy at the desired ultrasonic frequency. The ultrasonic transducer converts the electrical energy from the ultrasonic generator into mechanical vibrations.

Ultrasonic generator: The ultrasonic generator converts electrical energy from the line which is typically alternating current at 50 or 60 Hz to electrical energy at the ultrasonic frequency. This is accomplished in a number of ways by various equipment manufacturers. Current ultrasonic generators nearly as use MOSFET technology.

There have been several relatively recent innovations in generator technology, which may enhance the effectiveness of ultrasonic cleaning equipment. These include square wave outputs, slowly or rapidly pulsing the ultrasonic energy on and off and modulating or ‘sweeping’ the frequency of the generator output around the central operating frequency.

(To be concluded)

The writer is director, Applications Engineering, Life-Care Equipments Pvt Ltd, Mumbai